The present invention relates to novel fusion proteins comprising placental protein 14 (PP14) and methods for making and using these fusion proteins. The fusion proteins are useful for immune cell proliferation and function.
The human immune system functions to protect organisms from infection and from foreign antigens by cellular and humoral mechanisms. The immune system consists of cells and molecules that function in an orchestrated fashion to detect and eliminate foreign substances within the body. Though infectious agents, such as viruses, bacteria, parasites and fungi, represent the primary targets of the immune system, other aberrant cells within patients, such as infected, transplanted and cancerous cells, constitute additional immune targets. The abnormal molecules, largely proteins, of these various cellular and acellular targets of the immune system are generally referred to as antigens. The immune system is endowed with the capacity to seek out and destroy antigens. Essential operational features of the immune system are its abilities to recognize an enormously diverse array of antigens, distinguish one antigen from another in a highly specific fashion, and mount a more vigorous response when confronted with the same antigen more than once.
There are two major arms to the immune system, supported by different types of cells called B-lymphocytes and T-lymphocytes (B-cells and T-cells). B-cells make antibodies when they encounter antigens, and in most instances, these antibodies are protective. In autoimmune diseases, however, some of the antibodies react with the individual""s tissues. When they deposit in tissue, they cause an inflammatory reaction and tissue damage. T-cells, like B-cells, are also activated when they encounter an antigen. As T-cells develop, they undergo a process called xe2x80x9cthymic education.xe2x80x9d During thymic education, more than 95% of the T-cells die. The T-cells that have had a T-cell receptor that can recognize and react with the individual""s own tissues (self antigens) are specifically eliminated. Some autoreactive T-cells escape the elimination process, however, and can initiate an immune response that results in autoimmune disease.
Autoimmune diseases are generally believed to result from inappropriate responses of the immune system. In many autoimmune diseases, the T-cells go astray and attack the body""s healthy tissues. These T-cells appear to target the antigenic substances present in specific tissues. The antigenic substances differ depending upon the disease and may change in the course of the disease. In autoimmune diseases, the immune system appears to have escaped its normal control; what follows is a sequence of immune reactions that eventually lead to tissue damage. Autoimmune diseases are typically chronic and require life-long treatment. These treatments tend to fall into two categories: the first category involves compounds for palliative treatment, such as anti-inflammatory agents and pain killers; the second category involves the administration of nonspecific immunosuppressants, which indiscriminately shut down multiple parts of the immune system. These immunosuppressants usually have serious toxicity and side effect problems with long-term use and suppress the ability of the immune system to fight infection.
Thus, treatment of allergies and autoimmune diseases has been based on modalities that are toxic to immune cells, that inhibit production of antibodies, or that inhibit the effects of mediators of the immune response. Drugs that allow the manipulation of soluble lymphokines that regulate the immune system would be of use in the treatment of autoimmune diseases and diseases resulting from uncontrolled proliferation of immune cells. PP14 is one such drug of interest.
Pregnancy is a normal state in which at least one aspect of the immune responsexe2x80x94reaction to foreign antigensxe2x80x94is suppressed in regard to paternal antigens expressed by the fetus. Reports dating back over a century have indicated that a substantial percentage of women with multiple sclerosis, rheumatoid arthritis and certain other autoimmune diseases experience complete or partial remission of disease symptoms in association with pregnancy, although disease manifestations recur postpartum. The expression of a variety of proteins, including PP14, is induced to high levels during pregnancy. PP14 is a major secretory protein of decidual tissue, where it comprises about 10% of the total soluble protein. PP14 is a naturally occurring protein detected at especially high levels in the amniotic fluid and blood of pregnant women, as well as in the seminal fluid of males. PP14 may account for at least some of the immune suppressive phenomena of pregnancy.
U.S. Pat. Nos. 5,039,521 and 5,256,411 disclose methods for treating immune system disorders in humans by administration of PP14, derivatives, fragments, or subunits thereof, or monoclonal antibodies thereto. Methods for inhibiting interleukin-1 are also disclosed. The ""411 patent discloses a form of PP14 which is a dimer of two non-covalently linked protein subunits. Neither of the patents teach or suggest the PP14 fusion proteins disclosed herein.
PP14 has been shown to have in vitro effects on inflammatory cytokine (IL-1 and IL-2) production and T-cell proliferation. These immunoregulatory activities are evident at protein concentrations similar to those found in the serum of pregnant women. Investigations into the immunological function and regulation of PP14 have been impeded by the lack of recombinant PP14 derivatives with demonstrated ability to inhibit T-cell function. Because of PP14 ""s immunoinhibitory capacity, stable and more effective forms of PP14 in the treatment of immune system disorders are desired.
The present invention is directed to a PP14 fusion protein for the treatment of immune system disorders. More specifically, the present invention is directed to a fusion protein comprising a first domain comprising one or more sequences of PP14, and a second domain comprising one or more sequences of the Fc portion of an immunoglobulin molecule, such as immunoglobulin IgG1. A preferred embodiment of this fusion protein is PP14xc2x7Fcxcex31. The present fusion proteins are recombinant derivatives that inhibit T-cell activation and, as discussed below, function in a manner superior to other forms of PP14. Methods for making and using the fusion proteins are also within the present scope.
The PP14 fusion proteins disclosed and claimed herein have been found to have unprecedented immunoregulatory capabilities. PP14 and its fusion proteins not only directly inhibit the activation of T-cells of the immune system, but do so by a unique xe2x80x9crheostaticxe2x80x9d mechanism whereby they desensitize signaling through the T-cell receptor. As a consequence, they are effective in the modulation and treatment of autoimmune and alloimmune diseases. This may stem, at least in part, from their ability to skew T cell responses towards TH2 cytokine responses and away from TH1 cytokine responses. Because PP14 exists at high levels in the blood and amniotic fluid of pregnant women, and the fetus is therefore literally bathed in it without the slightest harmful effect, PP14 and its fusion proteins are not believed to have toxicity or significant side effects.
The present PP14 fusion proteins and genetic sequences encoding the same are useful in the treatment of a wide variety of immune and inflammatory diseases and conditions. The versatility of the PP14 fusion proteins is believed to address numerous autoimmune and alloimmune diseases by addressing the core pathogenic mechanism of those autoimmune diseases, although the inventor does not wish to be bound by this. Significantly, the present PP14 fusion proteins modulate the body""s immune responses, versus shutting them down, as present autoimmune and alloimmune disease drugs do; this allows the body""s immune system to continue to protect itself from opportunistic diseases and infections. Thus, the present invention provides for modulating the T-cell receptor response commensurate with the need to down regulate the cytokine output that is causing the immune system to inappropriately attack healthy cells, while at the same time allowing the immune system to protect the individual by retaining a sufficient degree of immune protection against infectious agents.
One aspect of the invention therefore is to provide PP14 in the form of fusion proteins.
Another aspect of the invention is to provide such proteins for use in the treatment of immune system diseases.
These and other aspects of the invention will be apparent based upon the following disclosure and appended claims.